U.S. patent number 6,667,604 [Application Number 10/199,095] was granted by the patent office on 2003-12-23 for power supply circuit with continued power generation after switch turn-off.
This patent grant is currently assigned to Denso Corporation. Invention is credited to Akihiro Yanagisawa.
United States Patent |
6,667,604 |
Yanagisawa |
December 23, 2003 |
Power supply circuit with continued power generation after switch
turn-off
Abstract
A power supply circuit includes a constant voltage circuit and a
timer circuit. The constant voltage circuit generates a constant
voltage by regulating a base current of the first transistor via
the second transistor. The timer circuit includes a comparator, a
delay circuit and an OR circuit. The comparator determines a
condition of the IG switch, open or closed. The delay circuit
delays inputting an output of the comparator for a predetermined
period. The OR circuit outputs a signal to halt the constant
voltage generation when the outputs of the comparator and delay
circuits indicate that the IG switch is open. The timer circuit is
used to continue the constant voltage generation for a
predetermined period after the IG switch is opened.
Inventors: |
Yanagisawa; Akihiro (Toyohashi,
JP) |
Assignee: |
Denso Corporation (Kariya,
JP)
|
Family
ID: |
19060308 |
Appl.
No.: |
10/199,095 |
Filed: |
July 22, 2002 |
Foreign Application Priority Data
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Jul 27, 2001 [JP] |
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2001-227680 |
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Current U.S.
Class: |
323/274; 323/266;
323/303 |
Current CPC
Class: |
G05F
1/575 (20130101) |
Current International
Class: |
G05F
1/10 (20060101); G05F 1/575 (20060101); G05F
001/44 () |
Field of
Search: |
;323/273,274,275,282,284,303,266,269 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-10-225003 |
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Aug 1998 |
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JP |
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A-2001-175366 |
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Jun 2001 |
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JP |
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Primary Examiner: Vu; Bao Q.
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed is:
1. A power supply circuit for a power supply system having a power
source, a power supply line that is continuously supplied with
power from the power source, a power supply switching means, the
power supply circuit comprising: a constant voltage circuit
provided in the power supply line to generate a constant voltage
when the power supply switching means is closed; and a timer
circuit that inputs a voltage when the power supply switching means
is closed, wherein the timer circuit is constructed to continue
constant voltage generation of the constant voltage circuit for a
predetermined period after the power supply switching means is
opened, then to halt the constant voltage generation.
2. The power supply circuit as in claim 1, wherein the timer
circuit comprises: a determination circuit that determines a
condition of the power supply switching means; a delay circuit that
delays inputting an output of the determination circuit for a
predetermined period; and a logic circuit that outputs a signal to
disable the constant voltage generation of the constant voltage
circuit when the outputs of the determination circuit and delay
circuit both indicate a closure of the power supply switching
means.
3. The power supply circuit as in claim 1, further comprising:
another power supply line that is supplied with power from the
power source via the power supply switching means; and diodes
connected in each power supply line, wherein a power supply voltage
for constant voltage generation is inputted to the constant voltage
circuit through at least one of the power supply lines via the
diodes.
4. A power supply circuit for a power supply system having a power
source, a power supply line that is continuously supplied with
power from the power source, a power supply switching means, the
power supply circuit comprising: a first constant voltage circuit
that performs a constant voltage generation when the power supply
switching means is closed and outputs a first constant voltage; and
a second constant voltage circuit connected in the power supply
line and outputs a second constant voltage, wherein an operation of
the second constant voltage circuit is determined based on the
first constant voltage inputted form the first constant voltage
circuit to the second constant voltage circuit.
5. The power supply circuit as in claim 4, further comprising: a
timer circuit to which a voltage corresponding to the condition of
the power supply switching means is inputted, wherein the timer
circuit is constructed to continue constant voltage generation of
the first constant voltage circuit for a predetermined period after
the power supply switching means is opened, then to halt the
constant voltage generation.
6. The power supply circuit as in claim 4, wherein a power supply
voltage for the constant voltage generation is inputted to the
first and second constant voltage circuits via the power supply
line that are continuously supplied with power from the power
source.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference
Japanese Patent Application No. 2001-227680 filed on Jul. 27,
2001.
FIELD OF THE INVENTION
The present invention relates to a power supply circuit utilized
for a vehicular control device and continues power generation after
switch turn-off.
BACKGROUND OF THE INVENTION
In a power supply circuit used for a vehicular control device,
large capacitance is required for an output capacitor in a constant
voltage circuit. Moreover, connectors in the power supply circuit
may cause problems due to inadequate connection.
A power supply circuit that counters the above problem is proposed
in U.S. Pat. No. 6,084,384 (JP-A-11-266547). As shown in FIG. 4,
this power supply circuit includes a battery 61, the first power
supply line BATT, the second power supply line VB and a switching
device 62, which includes an ignition switch. The first power
supply line BATT is continuously supplied with power from the
battery 61. The second power supply line VB is supplied with power
from the battery 61 only when the switching device 62 is closed. A
primary constant voltage circuit 63 is connected to the second
power supply line VB and an auxiliary constant voltage circuit 64
is connected to the first power supply line BATT. The constant
voltage circuits 63 and 64 supply power to the third power supply
line DL.
The primary circuit 63 includes a transistor 63a and a constant
voltage control IC 63b. The auxiliary circuit 64 includes a
transistor 64a and a constant voltage control IC 64b. A halt
control circuit 65 is provided to continue operations of the
auxiliary circuit 64 for a predetermined period after power supply
to the second power supply line VB is cut off.
In the power supply circuit, power is normally supplied from the
primary circuit 63 to the third power supply line DL. After the
switching device 62 is opened, the power is supplied from the
auxiliary circuit 64 to the third power supply line DL. If the
second power supply line VB is momentarily shut down, a constant
voltage is supplied by the auxiliary circuit 64. The output voltage
of the auxiliary circuit 64 is adjusted lower than that of the
primary circuit 63.
However, when the power supply circuit is implemented on an IC
chip, a voltage drop in output voltage may occur. When the
switching device 62 is opened and constant voltage generation by
the primary circuit 63 is halted, the auxiliary circuit 64 starts a
constant voltage generation. During the period between the time
that the switching device 62 is opened and the time that the
auxiliary circuit 64 starts providing a sufficient voltage, a
voltage drop may occur. The dropped voltage may trigger a low
voltage reset.
As shown in FIG. 5, when the switching device 62 is switched from
ON (closed) to OFF (opened), the primary circuit 63 enters the
non-operating state and the auxiliary circuit 64 enters the
operating state. It takes for a while until the output voltage of
the auxiliary circuit 64 rises to a sufficient level. As a result,
the output voltage of the power supply circuit drops during that
period.
In some vehicular control devices, a plurality of constant voltage
circuits are provided in a power supply circuit to generate
constant voltages in each section. In recent years, the constant
voltage is lowered to cut back power consumption of an onboard
battery. For instance, a power supply circuit that produces
different constant voltages for sensors and a CPU has been
introduced. In such a power supply circuit, constant voltage
generation for each constant voltage circuit is controlled by
opening and closing a switching device such as an ignition switch.
Since requirements for reduction in power consumption and for
constant voltage variation will increase, it is preferable that the
circuit configuration is more simplified.
SUMMARY OF THE INVENTION
The present invention therefore has an objective to provide a power
supply circuit that implements desired constant voltage generation
with a simple configuration.
The present invention has another objective to simplify the
configuration of the power supply circuit that outputs a variety of
constant voltages.
The power supply circuit of the present invention includes a
constant voltage circuit provided in a power supply line that is
continuously supplied with power from a power source. When a power
supply switching device is closed, the constant power supply
circuit performs constant voltage generation. The power supply
circuit also includes a timer circuit. The timer circuit controls
the constant voltage circuit to continue the constant voltage
generation for a predetermined period (allowable period) after the
switching device is opened.
If an instantaneous power interruption occurs and the interrupted
period is shorter than the allowable period, the constant voltage
generation continues. Therefore, the constant voltage is outputted
without interruption. When the interrupted period reaches the
allowable period, the constant voltage generation is halted.
The power supply circuit of the present invention does not require
a large-capacitance output capacitor to handle the instantaneous
power interruption. Since the power supply circuit of the present
invention does not require the switching, the voltage drop is
prevented. Therefore, a desired constant voltage generation by the
simple power supply circuit is possible.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objectives, features and advantages of the
present invention will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
FIG. 1 is a circuit diagram showing a power supply circuit
according to the first embodiment of the present invention;
FIG. 2 is a timing chart showing operations of the power supply
circuit according to the first embodiment of the present
invention;
FIG. 3 is a circuit diagram showing a power supply circuit
according to the second embodiment of the present invention;
FIG. 4 is a circuit diagram showing a power supply circuit
according to the related art; and
FIG. 5 is a timing chart showing a voltage drop occurring in the
power supply circuit of the related art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiments of the present invention will be
explained with reference to the accompanying drawings.
[First Embodiment]
Referring to FIG. 1, a power supply circuit 10 is directly
connected to a battery 1 to be continuously supplied with power
from the battery 1 via the first power supply line BATT. It is also
connected to the battery 1 through an ignition (IG) switch 2 to be
supplied with power from the battery 1 via the second power supply
line VB only when the IG switch 2 is closed. The IG switch 2 is a
power supply switching device and can be other types of switching
device such as a relay.
The power supply circuit 10 includes a constant voltage circuit 20
and a timer circuit 30. A power voltage is inputted to the constant
voltage circuit 20 via a diode 11 in the first line BATT or a diode
12 in the second line VB. Then, the constant voltage circuit 20
generates a predetermined constant voltage VOM (e.g., 5 V). An
output capacitor 13 is provided for the constant voltage circuit
20.
The constant voltage circuit 20 includes a pnp transistor 21 and a
npn transistor 22. The pnp transistor 21 is connected in the first
line BATT. The npn transistor 22 is connected to the base of the
pnp transistor 21. The constant voltage VOM is generated by
regulating a base current of the transistor 21 via the transistor
22. An output terminal of an operational amplifier 24 is connected
to the base of the transistor 22 via a switch 23. Non-inverting and
inverting terminals of the amplifier 24 are connected to a
reference voltage supply 25 and a middle point of a voltage divider
comprising resistors 26 and 27, respectively. The resistors 26 and
27 are utilized to feed back a fraction of the constant voltage VOM
to the amplifier 24.
The timer circuit 30 includes a voltage divider constructed of
resistors 31 and 32. The voltage divider is connected to the second
line VB. Non-inverting and inverting terminals of a comparator 33
are connected to a middle point of the voltage divider and a
reference voltage supply 34, respectively. An output of the
comparator 33 is divided into two; one is directly inputted to an
OR circuit 36 and the other is inputted to the OR circuit 36 via a
delay circuit 35. The switch 23 is opened or closed based on an
output of the OR circuit 36. In other words, constant voltage
generation is controlled by the output of the OR circuit 36.
The delay circuit 35 delays inputting an output signal of the
comparator 33 to the OR circuit 36 for a certain period of time. A
conventional circuit such as a flip-flop can be used for the delay
circuit 35. A delay time THD of the delay circuit 35 is set based
on an instantaneous interruption tolerance dose or a capacity of
the output capacitor 13. The comparator 33 corresponds to a
determination circuit for determining a condition of the switch 23
(open or closed). The OR circuit corresponds to a logic circuit
that outputs a signal to halt constant voltage generation.
Referring to FIG. 2, the IG switch 2 is assumed to switch from OFF
to ON and the voltage VB starts to increase from 0 V to 14 V at
time t1. At time t2, the voltage VB reaches a threshold voltage
Vth. As a result, a voltage measured at the non-inverting terminal
of the comparator 33 exceeds the reference voltage and the output
of the comparator 33 becomes high (H). At time t2, the output of
the timer circuit 30 (OR circuit 36) becomes high (H). Because of
this high signal, the switch 23 is closed and the constant voltage
VOM starts rising to a higher level. The timing at which the output
of the delay circuit 35 rises is later by the delay time THD (e.g.,
20 msec) than the timing at which the output of the comparator 33
rises.
It is assumed that at time t3, the voltage VB is instantaneously
interrupted due to the IG switch or power supply terminal connector
having a connection failure. During the period of TA, the output of
the comparator 33 becomes low. If the instantaneous power
interruption is temporary and the period TA is shorter than the
delay time THD, the output of the timer circuit 30 remains high and
the constant voltage VOM generation continues.
When the IG switch switches to OFF at time t4, the voltage VB
decreases. When the voltage VB becomes lower than the threshold
voltage Vth at the time t5, the output of the comparator 33 becomes
low. At the time t6, which is later by the delay time THD than the
time t5, the outputs of the delay circuit 35 and timer circuit 30
become low. Because of this low signal, the switch 23 switches to
OFF and the constant voltage generation is halted. Therefore, the
constant voltage VOM falls to a low level.
In FIG. 2, the same threshold voltage Vth is used in both cases
that the voltage VB is rising and falling for expediency. In real
application, the threshold voltage Vth preferably has hysteresis.
It is preferable to switch the threshold voltage Vth to a lower
level for the rising voltage and to a lower lever for the falling
voltage.
The power supply circuit 10 does not require a large-capacitance
output capacitor to counter to the instantaneous power
interruption.
The two power supply lines BATT and VB are provided to supply the
battery voltage to the constant voltage circuit 20 via the diodes
11 and 12. This makes the power supply circuit 10 highly
reliable.
[Second Embodiment]
Referring to FIG. 3, a power supply circuit 40 has the same
configuration as the power supply circuit 10 of the first
embodiment except for a constant voltage circuit 50. The first
constant voltage circuit 20 generates the first constant voltage
VOM (5 V) and the second constant voltage circuit 50 generates the
second constant voltage VOS (3.3 V). The output capacitors for the
constant voltage circuits 20 and 50 are not shown in FIG. 3 for
convenience.
A power supply voltage necessary for constant voltage generation is
inputted to the first and second constant voltage circuits 20 and
50. The voltage is inputted to the circuit 20 and 50 via a power
supply line BATT that is continuously supplied with power from the
battery 1.
The constant voltage circuit 50 has a pnp transistor 51 and a npn
transistor 52. The transistor 51 is connected in the first power
supply line BATT and the transistor 52 is connected to the base of
the transistor 51. A constant voltage VOS (3.3 V) is generated by
regulating a base current of the transistor 51 via the transistor
52. An output terminal of an operational amplifier 54 is connected
to the base of the transistor 52 via a switch 53. A constant
voltage supply is connected to the non-inverting terminal of the
amplifier 54. A middle point of the voltage divider constructed of
resistors 56 and 57 is connected to the inverting terminal of the
amplifier 54.
The switch 53 is opened or closed based on the constant voltage VOM
outputted from the constant voltage circuit 20. If VOM=5 V, the
switch 53 is closed and the constant voltage VOS is generated. If
VOM=0 V, the switch 53 is opened and the generation of constant
voltage VOS is halted.
In this embodiment, start and halt of the constant voltage
generation by the constant voltage circuit 50 are appropriately
controlled by the constant voltage VOM. Complicated configuration
is not required to determine whether the constant voltage
generation needs to be started or halted. Therefore, the power
supply circuit 40 has simple configuration even though it outputs
multiple constant voltages.
Since the power supply circuit 40 has the timer circuit 30, the
constant voltage generation continues in the case of instantaneous
power interruption. The constant voltage circuit 50 can also have
the same function. The power supply circuit does not require a
complicated configuration to provide desired constant voltage
generation.
The present invention should not be limited to the embodiment
previously discussed and shown in the figures, but may be
implemented in various ways without departing from the spirit of
the invention. For instance, the constant voltages (first and
second constant voltages) VOM and VOS can be the same voltages or
different voltages. The constant voltage VOS can be more than one.
In this case, a plurality of the constant voltage circuits having
the same configuration as the constant voltage circuit 50 is
provided as required. Start and halt of constant voltage generation
by the constant voltage circuits are controlled based on the
constant voltage VOM.
In FIGS. 1 and 3, the power supply lines BATT and VB are connected
to the diodes 11 and 12. The configuration can be modified as long
as power required for constant voltage generation is supplied to
the constant voltage circuit 20 via the first line BATT.
* * * * *